Method of purifying isobutylene by sulfuric acid extraction



Jan. 1, 1952 w A ARNOLD 2,581,065

METHOD OF uR'IFYING ISOBUTYLENE. BY SULFURIC ACID EXTRACTION Filed July 7, 1948 FRACTIONATOR.

CONDENSER Q \J 3 J] n O QEeENEQAi-orz m V T 4 0* 00 7F w I VENT IDIZUM l bx i v A l 6 N f {I ]L Q C/J'EzZtr CZ. (Zr-mold Sax/eater b /MQLQ L+Q Patented Jan. 1, 1952 METHOD OF PURIFYING IsoBU'rYLEnE BJY SULFURIQ'ACID EXTRACTION OFFICE Walter A. Arnold, .Songeigerong, Palembang, Sumatra, Netherland East Indies, assignor to Standard Oil De elopment Company, a corporation of Delaware amaican Jul 1948, Serial No. 37,398 I 1 o Claims; (01.260-677) This invention relates to the production'of isobutylene and particularly to the production of isobutylene free of other C4 hydrocarbons, particularly, butene-L' The invention is adapted to the production of isobutylene by absorptionbf (lo-hydrocarbon fractions in acid to form an extract and subseqent regeneration of isobutylene therefrom.

Isobutylene' is most satisfactorily separated from C r-hydrocarbon fractions derived by crackof these hydrocarbons has been sought. Another ing petroleum or from other sources by absorpdisadvantage, occurring in the operation of the tion of the O l-hydrocarbon stream in acid of 55 vacuum vent drum. is the tendency of the exto 70-weight per; centstrength, such as the polytract to produce considerable foam, which causes basic mineral acids, for example, sulfuric acid, carry-over of large amounts of the extract into phosphoric-acid, or the polybasic mineral acidthe hydrocarbon vent stream. acting acids, such as benzenesulfonic acid, tolu- It is an object of-this invention, therefore, to enesulfonic acid etc. g eliminate foaming and to reduce solubility of the An isobutylene-sulfuric acid extract may be dissolved gases when an isobutylene sulfuric exproduced by extracting a C r-hydrocarbon cut conraet ofhigh saturation is subjected to pressure taining isobutylene, butene-l, butene-2, isobu reduction in a vent drum to remove contaminants,

tane, normal butane, butadiene and small percentages of C3 and cs-hydrocarbons with 55 to '70 weight per cent sulfuric acid at temperatures in the range of approximately 60 to 120F. and pressures of 80 to 150 p. s. i. g. Under these conditions the sulfuric acid extracts the isobutylene fairly selectively. When an extract, prepared in this manner, is subjected to heating under controlled conditions, such as by stripping with steam,inert gases, such as nitrogen, light hydrocarbons, such as pentane etc., or with heavier inert hydrocarbons which are normally liquid, the isobutylene may be regenerated from the extract in relatively pure form. In the extraction operation; however, small percentages of butene-l and butene-2 also react with the acid and are present in the final extract. Also, the acid extract exhibits some solubility for other ci-hydrocarbons and mechanically entrains a portion of all hy-- drocarbons coming into contact with the acid. These hydrocarbons include the (li-paraflins and also the normal butenes. This physical solubil-- ity and entrainment is especially high when operating to produce extracts of high saturation, for example, 1.0-1.5 mols of olefin per mol of acid.

Since it is the object of the isobutylene'production process to produce an isobutylene stream of maximum purit it is imperative that the C4- paraffins and normal butenes be removed as thoroughly as possible therefrom. Removal of these contaminants has been carried out in the past by vacuum venting the extract before regeneration. This is accomplished by subjecting the extract to a flashing, operation to a vacuum of 1 to 14 p, s. i. absolute, preferably 10 p. s. i. absolute.

The means of inducing this'vacuum is to pass the extractthrough an efiicient flash zone, having a vapor outlet connection'to the suction of a compressor, steam jet etc. However, it has been found that vacuum venting produces only a partial removal of physically dissolved and entrained hydrocarbons; particularly, when the extract is one othigh saturation as indicated. Hence, a process which will permit more complete removal such as the cr-paramns, butadiene, the normal butenes and'hydrocarbon polymers thereof.

Accordingto this invention, foaming is eliminated and more complete removal of physically dissolved and mechanically entrained hydrocarbons is accomplished during the vacuum venting of an isob'utylene acid extract by adding to the extract, prior to or during the vacuum venting operation, tertiary butyl alcohol or an aqueous solution of tertiary butyl alcohol. The-tertiary butyl alcohol may be added to the extract feed to the vent drum, or more preferably,*the tertiary butyl alcohol may be added in the form of a spray to the top of the vent drum.

According to the invention, therefore, an isobutylene extract is produced by extracting a C4 cut containing isobutylene, butene-l, butene-2, saturated butanes'and butadiene and small percentages of Ca and Ct-hydrocarbons with an acid, such as sulfuric acid of about to weight per cent concentration, and'preferably, sulfuric acid of 60 to '70 weight per centconcentration; The acid at temperatures of 60 F. to 120 F. and pressures of approximately to 150 p. s. i. g. extracts the desiredisobutylene'fairly selectively. However, other hydrocarbons become physically dissolved'ormechanically entrained in the extract as previously recited. The acid extract leaves the absorber at about p. s. i. g. and is'allowed to settle into two layers. 'A spent'hydrocarbonlayer, which is removed; and an-acid extract layer; The settling operation takes place at approximately 70; to '80 p. s.'i. giyhence, considerable gas is dissolved in the resulting extract. The settled extract is then passed to a' vacuum vent drum,'f

as previously described, and still under pressure,

is led via line I into vent drum 2. Prior to in-' troduction of the extract into theventdrum, ter-'- tiary butyl alcohol or an aqueous somuo'nthere 1 of, may be added to the extract via line i5. In

the vent drum the pressure on the extract 7 reduced from '70 to 80 lbs. to pressures of i to 14 p. s. i. absolute, preferably, 10 p. s. i. absolute.

This sudden reduction in pressure, plus the fact that steam is added to the vent drum via coil l8 to raise the temperature from approximately 100 F. to 110 to 112 :52, cause physically dissolved and mechanically entrained gases to disengage. In the disengaging operation, ashormally carried out in the absence of tertiary butyl alcohol, the extract is caused to roain'up, often to the extent that it will passoverhead with the vented gases, causing'loss of the valuable extract and contaminating the hydrocarbon stream with acid. However, in the presence of the tertiary butyl alcohol, the foaming is suppressed so that gases disengage rapidly without the ,forma tion of a stable foam. The tertiary butyl alcohol also reduces the solubility of the gases in the extract so that they will more readily disengage therefrom. When the tertiary butyl alcohol is added to the vent drumthrough line 3 in the form of a spray, the alcohol additionally assists in the physical destruction of any foam which may form, although the alcohol itself serves as an agent to reduce surface-tension and to minimize foam formation regardless of its point of addition. Vent gases, including the saturated C4-hYd1'OCHJZ'bOnS, the normal butenes and butadiene, together with some li ht polymers thereof, pass overhead from the'vent drum via line 4.- The vented extract is then led via line 5 to regenerator 10. Prior to introduction; of the extract into the regenerator, it is diluted with water added via line 1 until the sulfuric acid is reduced toapproximatelydd to48 weight per cent concentration. In the regenerator a stripping operation occurs by means of-, steam;-or otherinert gas'added through line, The prod-1 uct takenover-head from the regenerator' via line 9 contains isobutylene, water, tertiary butyl alco-. hol, traces of secondary butyl alcohol and some hydrocarbon polymers. --,Weal spent acid; is .re-

moved from the regenerator, via line, 10 The overhead vaporproduct from the regenerator is condensed in partial condenser H in which gaseous isobutylene is separated from the water, tertiary butyl alcohol, secondary butyl alcohol and polymerswhich are removed via line 6. The tertiary butyl alcohol formed inthe regeneration process is an excellent source of. material to be addedto the vent drum according to this invention. However, the recycle product obtained as bottoms from the condenser should,

be substantially purified of large amounts of secondary butyl alcohol and hydrocarbon polymer before being recycledto the acid extract via line l6. Secondarybutylalcohol is not desir able in the tertiary butyl alcohol because it decomposes to butene-l and butene-2 during a the.

ventingbperation, thus causing possible, contamination ,of thedesired isobutylene product. The isobutylene stream is allowed to pass overadded to the vent drum via line I! and line 3 where it enters the 'vent drum in the form of The tertiary butyl alcohol employed in the vention-may be pure tertiary butyl alcohol or an acne us solution or tertiary butyl alcohol containing small amounts of water and other impurities; such as secondary butyl alcohol and hydrocarbon polymers. However, these impurities, as previously related, should be held to a very small amount. The amount of tertiary butyl alcohol employed in the rear drum may vary approximately between 5 and 20 weight per cent, preferably, 8 to 12 weight per cent based on the weight of acid extract.

' Eidmpl'e I t The efficiency of the isobutylene regeneration process, when carriedout according to the terms of the present invention, can be realizedfrom the following data. Y c c Upon the addition of tertiary butyl alcohol to the vent drum a commercial plant size isobu' tylene prod ction process, it possible to increase the (it-hydrocarbon feed to theabsorber from about 400,000 to about 600,000 lbs. per day. This increase is, of course, possible because of the more rapidand complete removalof the vent gases from thevent drum and also because ofthe elimination of substantiatfoarning in the vent drum. At the same time, the production of isobutylene was increased from 13' tonser day to a figure between '23 and 44 tonsper day. These results were produced by employing approxi mately 11,000 to 15,000lbs. per hourof' recycle tertiary bu'tyl alcohol; containing approximately vol. percent tertiarybutyl alcohol, 10% water. and the balance impurities, chiefly, Ci polymers and secondary butyl alcohol. The acid extract feed rate to the vent drum, to produce-the above improved conditions, was increased 7 to about 12,100 lbs. of extract persh'o'ur. The extract sat uration was approximately 10-.7v to -1.5 ormore mols of, isobutylene per mol of sulfuric acid in sulfuric acidof 65 weight percent strength on a: hydrocarbon free basis-r. l c

Having described the invention ina manner so; that itmay be practiced by those skilled in the art, whatis claimedis: I

1. A process for the prcduction'of isobutylene whichcomprises contacting a (Er-hydrocarbon stream containing isobutylene, normal butenes,

butanes-andbutadiene at atemperature of 60 to i Flandat a pressure of 80 to .p. s. i. g.

with an acidto forman isobutyleneacid extraca.

adding tertiary bu'tyl alcohol to the extractin a vent drum while still under pressure, reducing.

A process accordingto claim 1' in which the. acid is sulfuric acid of..; 55, to 70' weight pcrcent concentration.

acsnoca 3. A process according to claim 1 in which the acid is sulfuric acid of 65 weight percent concentration.

4. A process according to claim 1 in which the tertiary butyl alcohol is added to the vent drum in the form of a spray.

5. A process according to claim 1 in which the tertiary butyl alcohol is added in amounts of 5 to 20 weight percent based on the weight of acid extract in the vent drum.

6. A process according to claim 1 in which the tertiary butyl alcohol is added in amounts of 8 to 12 weight percent based on the weight of acid extract in the vent drum.

7. A process according to claim 1 in which the tertiary butyl alcohol added to the vent drum is an aqueous solution of tertiary butyl alcohol, containing approximately 80 volume percent tertiary butyl alcohol.

8. A process for purifying an isobutylene-acid extract contaminated with physically dissolved and mechanically entrained normal butenes, bu-

tanes and butadiene, which comprises adding tertiary butyl alcohol to the extract while under pressure of 80 to 150 p. s. i. g., and thereafter reducing the pressure on the extract to approximately 1 to 14 p. s. i. absolute, whereby the physmany dissolved and mechanically entrained normal butenes, butanes and butadiene are removed from the isobutylene-acid extract.

9. A process according to claim 8 in which the isobutylene-acid extract is an isobutylene-suliuric acid extract.

10. A process according to claim 8 in which the tertiary butyl alcohol added to the extract is an aqueous solution of tertiary butyl alcohol, containing approximately volume percent tertiary butyl alcohol.

WALTER A. ARNOLD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,268 Bannon et a1. Feb. 16, 1943 2,014,078 Archibald et al. Sept. 10, 1935 2,400,340 Cone May 14, 1946 2,400,376 Showalter May 14, 1946 2,431,005 Willauer et a1 Nov. 18, 1947 2,456,260 Draeger Dec. 14, 1948 2,497,191

Steele et a1. Feb. 14, 1950 

1. A PROCESS FOR THE PRODUCTION OF ISOBUTYLENE WHICH COMPRISES CONTACTING A C4F-HYDROCARBON STREAM CONTAINING ISOBUTYLENE, NORMAL BUTENES, BUTANES AND BUTADIENE AT A TEMPERATURE OF 60 TO 120* F. AND AT A PRESSURE OF 80 TO 150 P.S.I.G. WITH AN ACID TO FORM AN ISOBUTYLENE ACID EXTRACT, ADDING TERTIARY BUTYL ALCOHOL TO THE EXTRACT IN A VENT DRUM WHILE STILL UNDER PRESSURE, REDUCING THE PRESSURE ON THE EXTRACT TO APPROXIMATELY 1 TO 14 P.S.I. ABSOLUTE, WHEREBY PHYSICALLY DISSOLVED AND MECHANICALLY ENTRAINED HYDROCARBONS, INCLUDING NORMAL BUTENES, BUTANES AND BUTADIENE, ARE RELEASED FROM THE EXTRACT, AND THEREAFTER RECOVERING ISOBUTYLENE FROM THE ACID EXTRACT. 